Method of calibrating clutches in transmissions

ABSTRACT

A microprocessor controlling a shuttle shift transmission may be programmed to effect a calibration of the final drive clutches in the transmission so that the microprocessor can efficiently effect engagement of each respective said clutch by applying the proper hydraulic pressure to cause proper engagement thereof. This method of calibrating the final drive clutches in the transmission includes braking the output shaft of the transmission so that any engagement of the selected final drive clutch being calibrated will cause a load to be applied to the engine. The hydraulic pressure is then incrementally increased until the engine RPM&#39;s decrease because of the load being placed on the engine. The value of this engagement hydraulic pressure is stored in the microprocessor for use when effecting engagement of the selected clutch during operation of the transmission. Service indicators are programmed into the microprocessor should the selected clutch not be capable of being calibrated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. Patent Application Serial No.444,312, filed on Dec. 1, 1989 now allowed.

BACKGROUND OF THE INVENTION

Power shift transmissions are well known in the art. Some power shifttransmissions provide shuttle shift capability which permits the vehicleto change direction of operation without requiring the movement of thegearshift lever through each intermediate gear ratio. To accomplish thisoperation, these known types of shuttle shift transmissions willtypically include torque converters. In such transmissions utilizingtorque converters for shuttle shifting at high or even moderate speeds,a high energy load is placed on the clutches.

Some power shift transmissions are characterized in that they do notrequire a different gearshift lever position for each gear ratio whichmay be selected. While such transmissions have simplified operatorcontrol, such transmissions do have drawbacks and lack certain desirablefeatures. For example, these transmissions provide automatic speed ratiomatching with no means permitting an operator to intervene manually inthe automatic speed ratio matching process.

The operation or response of the transmission clutches vary from onetransmission to another, or in a given transmission over a period oftime. The present invention alleviates some of these problems and, inaddition, provides new methods by which an operator may effect theshuttle shifting process.

SUMMARY OF THE INVENTION

An object of the invention is to provide novel methods of controllingvehicle deceleration during shuttle shifting to thereby reduce theenergy input to the clutches. According to a first method, clutches inthe transmission are set to select the lowest gear and one clutch has amodulating signal applied thereto whereby the transmission and engineact as a brake. The speed of the output shaft is monitored and as itapproaches zero the clutches are set to select the desired gear.

In a second method of controlling deceleration, clutches are released todisconnect the transmission from the engine. Next, at least two clutchesare set to lock up the transmission. A modulating signal is then appliedto one clutch to vary the load the transmission places on the outputshaft. the output shaft speed is monitored and as it approaches zero theclutches are selectively energized to select the new gear.

In a third method of controlling deceleration the rotation of the inputand output shafts of the transmission are monitored and the clutches areset to the lowest gear which does not overspeed the engine. As the speedof the output shaft drops, successively lower gears are selected.

A further object of the invention is to provide a method whereby anoperator may, by operation of the gearshift lever, override a programwhich provides automatic speed ratio matching during shuttle shifting.

Another object of the invention is to provide a method whereby anoperator may pre-program a desired ratio between the forward and reversegears selected during shuttle shifting.

Another object of the invention is to provide a method whereby, whilethe gearshift lever is in neutral, the operator may preselect a desiredgear into which the transmission will be shifted upon subsequentmovement of the gearshift lever to the forward or the reverse position.

Yet another object of the invention is to provide a novel method ofproducing a value representing a calibration signal for a clutch, saidcalibration signal being added to the clutch modulating signal toprovide a uniform operation of the clutch.

Other objects of the invention and its mode of operation will becomeapparent upon consideration of the following description and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a shuttle shift transmission controlsystem of the prior art;

FIG. 2 the shift pattern for a gearshift lever;

FIG. 3 is a schematic planar development of the three-dimensionaltransmission shown in FIGS. 4-9.

FIG. 4 is a schematic plotting of the transmission layout showing thelocations of the shaft centers, corresponding to lines 4--4 of FIG. 3;

FIG. 5 is a schematic plotting of the locations and relationships of theprimary drive gear set corresponding to lines 5--5 of FIG. 3;

FIG. 6 is a schematic plotting of the locations and relationships of thefixed gears mounted on the first, second and third jack shaftscorresponding to lines 6-6 of FIG. 3;

FIG. 7 is a schematic plotting of the locations and relationships of theintermediate gear set mounted on the first, second and third jack shaftscorresponding to lines 7--7 of FIG. 3;

FIG. 8 is a schematic plotting of the locations and relationships of thetransfer gears corresponding to lines 8-8 of FIG. 3;

FIG. 9 is a schematic plotting of the locations and relationships of thefinal drive gear set corresponding to lines 9--9 of FIG. 3;

FIG. 10 illustrates a gearshift pattern according to one aspect of thepresent invention;

FIG. 11 is a flow diagram of a program executed by the microprocessor ofFIG. 1 to preselect a gear;

FIG. 12 a flow diagram illustrating a method of preselection of aforward to reverse gear ratio prior to starting a vehicle;

FIG. 13 is a subroutine for the preselection of a forward to reversegear ratio;

FIGS. 14a and 14b illustrate routines for selecting reverse and forwardgears, respectively, using the ratio developed by the subroutine of FIG.13;

FIG. 15 is a flow diagram illustrating a first method of controllingvehicle deceleration during the shifting of gears;

FIG. 16 is a flow diagram illustrating a second method of controllingvehicle deceleration during the shifting of gears;

FIG. 17 is a flow diagram illustrating a third method of controllingvehicle deceleration during the shifting of gears;

FIG. 18 is a flow diagram illustrating a first method of calibratingclutches;

FIG. 19 is a flow diagram illustrating a second method of calibratingclutches;

FIGS. 20a and 20b are flow diagrams illustrating methods for manuallyoverriding the automatic ratio matching feature for a power shifttransmission, the method of FIG. 20b resulting in a temporary overridefor a specific interval of time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-9 illustrate a power shift transmission system of the prior art.As shown in FIG. 1, the power shift transmission control system includesa microprocessor 1, a display 2 on an operator's control panel 2', aplurality of gearshift switches 4 which are selectively actuated bymanually moving a gearshift lever 6, and a plurality of transmissionclutches 8 associated with a transmission 10 which transmits power froma rotating power input shaft 15 to a power output or vehicle drive shaft20. An engine 7 unidirectionally rotates shaft 15 and a sensor 9 sensesrotation of shaft 15 to provide output signals indicating the speed ofengine 7. A sensor 5 senses rotation of shaft 20 to provide outputsignals representing vehicle speed. An operator-actuated clutch pedal 3controls a potentiometer 3' and the output signal from the potentiometeris applied to microprocessor 1 to develop modulating signals which areapplied to a final set of clutches in transmission 10. The clutch pedal3 also actuates a clutch pedal switch CPSW when the pedal is depressedto its limit of travel. The control system is admirably suited forcontrolling the transmission of a tractor but it will be obvious fromthe following description that it may also be used to control thetransmissions of other vehicles or machines.

The gearshift switches 4 are Hall-effect switches or similar deviceswhich are actuated by a magnet or magnets carried on the gearshift lever6. Microprocessor 1 periodically samples the clutch pedal switch, theoutput of potentiometer 3', the switches 4, and the outputs of the speedsensors 5 and 9, and in response to the sensed conditions controlstransmission clutches 8 to "select gears", i.e. select the direction andrate of rotation of output shaft 20 relative to input shaft 15.

FIG. 2 is a plan view of the path over which the gearshift lever 6 maybe manually moved to selectively actuate the gearshift switches 4. Thelever 6 is shown in the neutral position N. In this position themicroprocessor controls the transmission clutches 8 so that no power istransmitted from input shaft 15 to output shaft 20. The microprocessoralso controls the display 2 so that the letter N is displayed,indicating to the operator that the transmission is in neutral.

The gearshift lever 6 may be moved forwardly (upwardly in FIG. 2) fromthe neutral position to a forward position F. When the microprocessorsenses that the gearshift lever is the forward position it energizesclutches 8 so that rotation of the power input shaft is transmitted tothe output shaft in one of eighteen different forward speed ratios. Themanner in which this is accomplished will be evident from thedescription of transmission 10 set forth below. At the same time, themicroprocessor sends signals to display 2 so that it displays the letterF and a numeric value between one and eighteen. The display thusindicates to the operator that his transmission is in a forward gear,and further indicates which gear.

When the gearshift lever 6 is in the forward position F it may be movedlaterally to change forward gears. When the gearshift lever 6 is movedto its rightmost extent of travel in the forward position it actuates aswitch. This position is designated the FUP position. The microprocessor1 periodically samples the switches 4 and, when the gearshift lever 6 isin the FUP position, the microprocessor periodically changes theclutches 8 which are energized so that the speed ratio between outputshaft 20 and input shaft 15 increases. When the highest forward gear(18) is reached, the microprocessor continues to energize the clutches 8to keep the transmission in gear 18 even though the gearshift lever 6continues to actuate the FUP switch. As the microprocessor 1 controlsthe transmission clutches 8 it also controls the display 2 to indicateforward gear (F) and which forward gear (1-18) the transmission is in.

In like manner, the gearshift lever 6 may be moved laterally to the leftin the forward position to downshift the transmission. In the forwarddownshift position FDN the lever 6 actuates one of gearshift switches 4.The microprocessor periodically downshifts the transmission 10 bycontrolling clutches 8, and as the transmission is shifted downwardlythe microprocessor controls display 2 to indicate that the transmissionis in forward gear and which forward gear. By holding the lever 6 in theforward downshift position the operator may downshift the transmissionone gear at a time until forward gear 1 is reached. At this time, themicroprocessor continues to output signals to the transmission clutches8 to select forward gear 1 even though the gearshift lever 6 is held inthe FDN position .

When the gearshift lever 6 is in the reverse position R, it may be movedlaterally to the right to increase the reverse gear speed ratio oftransmission 10, or moved laterally to the left to decrease the reversegear speed ratio. At each limit of travel, designated the RUP and RDNpositions respectively, gearshift switches 4 are actuated to control themicroprocessor 1 for upshifting or downshifting the reverse gear speed.As long as the gearshift lever is in the reverse position the display 2displays the letter R to indicate reverse gear and also displays anumber between 4 and 12 indicating which reverse gear the transmissionis in. There are 9 reverse gears, the lowest being fourth gear and thehighest being twelfth gear.

The gearshift lever 6 is biased so that if it is in the FUP or FDNposition it returns to the F position when manual force is removed. Inlike manner, if the lever is in the RUP or RDN position and force isremoved, the lever returns to the R position. In addition, the gearshiftlever 6 is provided with a lift collar (not shown). In shifting betweenthe forward and reverse gear positions, the collar must be lifted.Otherwise, movement of the gearshift lever is stopped at the neutralposition.

FIGS. 3-9 illustrate details of the transmission 10. As shown in FIGS. 3and 4, the transmission 10 includes an exterior casing 12 forming aframework for supporting the power input shaft 15 rotatably journalledon the casing 12 at a central location extending entirely through thetransmission 10 from an engine end 16, which receives rotational powerdirectly from the engine 7, to a drive end 17 at the opposing end of thetransmission 10, which can be used as a power takeoff shaft. The centersof a power output shaft 20, a first jack shaft 21, a second jack shaft22, a third jack shaft 23, a fourth jack shaft 26, a fifth jack shaft28, and the shaft 55 of a double transfer gear are located in FIG. 4.Each of shafts 20, 21, 22, 23, 26, 28 and 55 is journalled by bearingsrotatably supporting the respective shafts for rotation within thecasing 12. The relationships between these various shafts and the gearsmounted thereon are described in greater detail below in conjunctionwith FIGS. 3 and 5-9.

Referring now to FIGS. 3 and 5, it can be seen that the power inputshaft 15 is provided with a drive pinion 18 splined thereto for rotationtherewith at the engine end 16 of the power input shaft 15. The drivepinion 18 is drivingly engaged with a primary drive gear set 30. Morespecifically, the drive pinion 18 is directly engaged with a first drivegear 31 rotatably mounted on the first jack shaft 21 for rotationindependently of said first shaft 21. The drive pinion 18 is alsodirectly engaged with a third drive gear 33 rotatably mounted on thethird jack shaft 23 for rotation relative thereto. The third drive gear33 is meshed in engagement with a second drive gear 32, which in turn isrotatably mounted on the second jack shaft 22. Each of the drive gears31, 32 and 33 is journalled by bearings mounted on their respective jackshafts and driven by the power input shaft 15 by virtue of direct orindirect engagement with the drive pinion 18. Each of the drive gears21, 22 and 23 is sized differently to provide different speeds ofrotation thereof when rotated by the drive pinion 18.

As can be seen in FIGS. 3 and 6, each of the jack shafts 21, 22 and 23is provided with a corresponding fixed gear 35, 36 and 37, respectively.The second fixed gear 36 is drivingly engaged with both the first fixedgear 35 and the third fixed gear 37 so that the rotation of any one ofthe jack shafts 21, 22 and 23 will effect a simultaneous rotation of allthe other jack shafts 21, 22 and 23. Since all the fixed gears 33, 36and 37 are identical in size, the first jack shaft 21, the second jackshaft 22 and the third shaft 23 will rotate at identical speeds.

As shown in FIGS. 3 and 7, the transmission 10 is also provided with anintermediate gear set 40 corresponding to the primary drive gear set 30and including a first intermediate gear 41 mounted on the first jackshaft 21 for rotation relative thereto, a second intermediate gear 42rotatably mounted on the second jack shaft 22, and a third intermediategear 43 rotatably supported on the third jack shaft 23. The intermediategears 41, 42 and 43 are differently sized to effect a different speedratio particularly when combined with the differently sized drive gears31, 32 and 33 of the primary drive gear set 30, as will be described ingreater detail below. The first and third intermediate gears 41, 43 areengaged with a transfer hub assembly 45 as will be described below,while the second intermediate gear 42 is drivingly engaged with thethird intermediate gear 43. Like the primary drive gear set 30, eachintermediate gear 41, 42 and 43 is journalled by bearings mounted on thecorresponding jack shaft 21, 22 and 23 to permit independent rotationtherebetween.

The intermediate gear set 40 is engaged with a transfer hub assembly 45rotatably supported from the casing 12 concentric with the power inputshaft 15. The transfer hub assembly 45 includes a first transfer gear 46drivingly engaged with the first intermediate gear 41 and a secondtransfer gear 47 drivingly engaged with the third intermediate gear 43.The transfer hub assembly 45 is also provided with a co-joined thirdtransfer gear 48 and fourth transfer gear 49 to transfer rotationalpower from the intermediate gear set 40 to a transfer gear set 50.

Referring to FIGS. 3 and 8, the third transfer gear 48 is drivinglyengaged with a reverse transfer gear 51 fixed to a fifth jack shaft 28rotatably supported in the casing 12. Likewise, a high-speed transfergear 53 is rotatably journalled on the power output shaft 20 and isdrivingly engaged with the fourth transfer gear 49 for rotationtherewith independently of the power output shaft 20 and is drivinglyengaged with the fourth transfer gear 49 for rotation therewithindependently of the power output shaft 20. A double transfer gear 55having a shaft-like configuration and integral gear members 55a and 55bis rotatably supported in the casing 12. The gear member 55a is alsodrivingly engaged with the fourth transfer gear 49, while the other gearmember 55b is engaged with a low-speed transfer gear 57 fixedly securedfor rotation with a fourth jack shaft 26 rotatably journalled in thecasing 12.

As can be best seen in FIGS. 3 and 9, a final drive gear set 60 includesa high-speed final gear 61 rigidly secured to the power output shaft 20for rotation therewith, a low-speed final gear 62 rotatably journalledby bearings on the fourth jack shaft 26 for rotation independentlyrelative thereto, and a reverse final gear 63 rotatably journalled onthe fifth jack shaft 58 for rotation relative thereto. The final drivegear set 60 is interengaged for simultaneous rotation such that thehigh-speed final gear 61 fixed to the power output shaft 20 isoperatively intermeshed with both the low-speed final gear 62 and thereverse final gear 63.

Referring now to FIG. 3, the transmission includes three clutch sets 70,75 and 80 operable to effect rotation of the various gears rotatablymounted on jack shafts with the corresponding shaft. The initial clutchset 70 includes a first clutch 71 mounted on the first jack shaft 21, asecond clutch 72 mounted on the second jack shaft 22 and a third clutch73 mounted on the third jack shaft 23. Each clutch 71, 72 73 of theinitial clutch set 70 is operable to engage the corresponding drive gear31, 32 and 33 to effect rotation of the corresponding jack shaft 21, 22and 23 with the corresponding drive gear 31, 32 and 33 at the speed thecorresponding drive gear is rotating. Likewise, an intermediate clutchset 75 includes first, second and third intermediate clutches 76, 77 and78, respectively, mounted on the first, second, and third jack shafts21, 22 and 23, respectively, for engagement with the correspondingintermediate gear 41, 42 and 43 at the speed a which the correspondingjack shaft is being driven.

A final clutch set 80 includes a high-speed final clutch 81 mounted onthe power output shaft 20 and engageable to couple the high-speedtransfer gear 53 to the high-speed final gear 61 when so engaged. Thefinal clutch set 80 also includes a low-speed final clutch 82 mounted onthe fourth jack shaft 26 to effect a coupling, when engaged, between thelow-speed transfer gear 57 and the low-speed final gear 62. Likewise,the final clutch set 80 also includes a reverse final clutch 83 mountedon the fifth jack shaft 28 for selectively coupling the reverse transfergear 51 to the reverse final gear 63. To attain any given speed ofrotation of the power output shaft 20 for a given speed of rotation ofthe power input shaft, only one selected clutch of each clutch set 70,75, 80 is engaged at a time. The engagement of two clutches of any oneclutch set 70, 75 and 80 will have the effect of locking thetransmission 10.

With all of the components of the transmission 10 situated as describedabove, transmission 10 can transmit a given engine speed received by theengine end 16 of the power input shaft 15 to the output shaft 20 intwenty-seven different speed variations with eighteen forward speeds andnine reverse speeds. It can be seen that the drive pinion 18 constantlydelivers rotational power from the engine to the primary gear set 30such that the first, second, and third drive gears 31, 32 and 33 areconstantly driven with the drive pinion 18 relative to the respectivejack shaft 21, 22 and 23 on which the gears of the primary drive gearset 30 are respectively mounted. The engagement of one of the clutches71, 72 and 73 of the initial clutch set 70 effects an engagement of thecorresponding drive gear 31, 32 or 33 with the respective jack shaft 21,22 or 23 and effects rotation of the jack shafts 21, 22 and 23 at thespeed at which the corresponding drive gear is being rotated. Since theintermeshed fixed gears 35, 36 and 37 are of identical size, rotation ofany one of the jack shafts 21, 22 and 23 will effect rotation of allthree jack shafts 21, 22 and 23 at identically the same speed as thedrive gear 31, 32 and 33 engaged by the selected clutch of the initialclutch set 70.

The engagement of one of the clutches of the initial clutch set 70 willeffect a corresponding rotation of the first, second, and third jackshafts 21, 22 and 23 at a selected speed corresponding to thecorresponding drive gear from the primary drive gear set 30. Asubsequent engagement of one of the clutches 76, 77 and 78 of theintermediate clutch set 75 will effect an engagement between thecorresponding intermediate gear from the intermediate gear set 40 withthe rotating jack shaft corresponding to the selected intermediateclutch at the speed at which the jack shafts 21, 22 and 23 are rotating.Since all of the intermediate gears of the intermediate gear set 40 areengaged with the transfer hub assembly 45, directly or indirectly, whichin turn is engaged with the transfer gear set 50, an engagement of oneof the clutches of the intermediate clutch set 75 will effect a rotationof all gears of the intermediate gear set 40, the transfer hub assembly45, all of the transfer gears 46, 47, 48 and 49 and all of the gears inthe transfer gear set 50, as well as the corresponding rotation of boththe fourth and fifth jack shafts 26, 28 due to a fixed engagement withthe corresponding transfer gears 51, 57.

Finally, an engagement of one of the clutches 81, 82 and 83 of the finalclutch set 80 will transfer rotational power from the correspondingtransfer gear to the corresponding final gear 61, 62 and 63 of the finaldrive gear set 60 to cause a rotation of the power output shaft 20 atthe speed ratio corresponding to the combination of the respective gearsengaged by the activated clutches of the initial clutch set 80.

By way of specific example, the engagement of the second clutch 72 ofthe initial clutch set 70 will couple the second drive gear 32 to thesecond jack shaft 22 and effect rotation of the first, second, and thirdjack shafts 21, 22 and 23 at the speed at which the second drive gear 32is being rotated due to engagement with the third drive gear 33 and thedriving engagement of the third drive gear 33 and the driving engagementof the third drive gear 33 with the drive pinion 18. In the examplebeing described, both the first and third drive gears 31, 33 rotate onthe corresponding jack shaft 21, 23 without transferring rotationalpower thereto. In fact, the engagement of the second clutch 72 willresult in a rotation of both the first and third jack shafts 21 and 23at a speed different than the speed at which either of the correspondingfirst and third drive gears 31, 33 is independently rotating.

By way of continuing the example started above, the subsequentengagement of the first intermediate clutch 76 drivingly couples thefirst intermediate gear 41 with the rotating first jack shaft 21 toeffect a corresponding rotation of the entire intermediate gear 41 withthe rotating first jack shaft 21 to effect a corresponding rotation ofthe entire intermediate gear set 40 due to the intermeshed engagementwith the first transfer gear 46 and resultant rotation of the secondtransfer gear 47 co-joined therewith, which in turn independentlyrotates the second and third intermediate gears 42, 43 on respectivejack shafts 22 and 23. As noted with the exemplary description abovewith respect to the primary drive gear set 30, the intermediate gears42, 43 rotate independently of the jack shafts 22 and 23 without drivingengagement therebetween because the corresponding clutches 77 and 78have not been engaged.

As noted above, the rotation of the transfer gears 46 and 47 cause acorresponding rotation of the entire transfer hub assembly 45 and effecta corresponding rotation of the entire transfer gear set 50, as well asthe fourth and fifth jack shafts 26 and 28. The selected combination ofthe second drive gear 32 and the first intermediate gear 41 effectsrotation of the reverse transfer gear 51, the high-speed transfer gear53, and the low-speed transfer gear 57 at a preselected ratio. As oneskilled in the art will readily realize, the different combinations ofengagements between the primary drive gear set 30 and the intermediategear set 40 provide for nine different speed ratios at which thetransfer gears 51, 53 and 57 are rotated.

Continuing the example started above, a final selection of the low-speedfinal clutch 82 will couple the rotation of the fourth jack shaft 26 andthe integral low-speed transfer gear 57 to the low-speed final gear 62.The intermeshed engagement between the low-speed final gear 62 and thehigh-speed final gear 61 will effect a rotation of the power outputshaft 20 at the predetermined speed corresponding to the combination ofclutch engagements described above. Since the reverse final clutch 83remains disengaged, the reverse final gear 63 can rotate harmlessly onthe fifth jack shaft 28 due to the engagement with the high-speed finalgear 61.

If, in the example given above, the high-speed final clutch 81 had beenselected for engagement rather than the low-speed final clutch 82, thehigh-speed final clutch 81 would have coupled the high-speed transfergear 53 to the high-speed final gear 61 to directly power the rotationof the power output shaft 20. The engagement of the high-speed finalclutch 81 means that neither the low-speed final clutch 82 nor thereverse final clutch 83 is engaged so low-speed final gear 62 and thereverse final gear 63 can rotate harmlessly on the respective jackshafts 26 and 28 on which they are mounted due to engagement with thehigh-speed gear 61.

The various combinations of the engagement of gears of both the primarydrive gear set 30 and the intermediate gear set 40 provides ninepossible speed ratios for rotation of the individual gears 61, 62 and 63of the final drive gear set 60. Accordingly, the above-describedtransmission will provide nine different low-range speeds for rotationof the power output shaft 20 when the low-speed final clutch 82 isengaged, as well as nine different high-range speeds when the high-speedfinal clutch 81 is selected, or nine different speeds of reverserotation of the power output shaft 20 if the reverse final clutch 83 isengaged.

The torque transmitting elements of the clutches intransmission 10 arehydraulically actuated to transfer torque. Solenoid operated valvescontrol the pressure applied to the clutches and thus the torquetransferred to the output shaft 20 to move the vehicle.

The electrical signals applied to the solenoids for the clutches 81, 82and 83 in the final clutch set 80 may be modulated to incrementally varythe pressure applied to the torque transmitting elements. As the clutchpedal 3 is depressed, the magnitude of the signal applied tomicroprocessor 1 from the potentiometer 3' varies. Using this signal,the microprocessor develops a pulse width modulated signal that isapplied to the solenoid of one of the clutches 81, 82 or 83 depending onwhich gear the transmission is in. When the clutch pedal 3 is fullydepressed, it actuates the clutch pedal switch CPSW. When microprocessor1 senses that CPSW is actuated it applies a signal to the solenoid ofone of the clutches 81, 82 or 83 so that no hydraulic pressure isapplied to the torque transmitting element of the clutch and no torqueis transmitted by the clutch.

Preselection of Gears

In accordance with one aspect of the present invention, a gear speed maybe selected any time the gearshift lever 6 is in the neutral position.Since the gearshift lever must be in neutral, the operator may devotefull attention to the gear selection process without compromisingsafety.

Preselection of a gear speed is made possible by providing for lateralmovement of the gearshift lever 6 in the neutral position as illustratedin FIG. 10. At its leftmost or rightmost extent of travel, designatedthe NDN and NUP positions, respectively, the gearshift lever 6 actuatesgearshift switches 4 to signal microprocessor 1 that it is in the NDN orNUP position.

Briefly, the operator accomplishes preselection of gears by placing thegearshift lever in neutral and selectively moving the gearshift leverbetween the NUP, NDN and N positions to increment or decrement thedisplayed gear value until it agrees with the gear he wishes to select.

FIG. 11 is a flow diagram of a suitable routine which may be executed bymicroprocessor 1 to effect preselection of gears. The routine is enteredat step 112 when the microprocessor 1 senses that the gearshift lever 6is in the N position. The display 2 is updated at step 114. At step 116the program waits for the operator to move the gearshift lever to theNUP or NDN position. At this point the display 2 will be displaying theletter N and a value representing the contents of a register PSG. Theregister PSG is a memory location in microprocessor 1 which stores avalue representing the gear last preselected.

Assume first that the operator wishes to increase the preselected gearvalue PSG to some value greater than the value being displayed bydisplay 2. He moves the gearshift lever from the N position to the NUPposition to exit step 116.

At step 122 the microprocessor tests the gearshift switches to see ifthe gearshift lever is in the NUP position. If the operator has movedthe gearshift lever to the NUP position, signifying that he wishes topreselect a higher numbered gear than that being displayed, the test atstep 122 proves true. The program advances to step 124 where the valueof PSG is tested. If the value is less than 18, the test at step 124proves false and the program moves to step 126 where the value in thePSG register is incremented by one and saved. At step 128 the display isupdated to display the new value in PSG.

After the display is updated, the program waits at step 130 for a fixedinterval of time, on the order of a fraction of a second. This waitprovides time for the operator to react and move the gearshift lever outof the NUP position as the value in the PSG register approaches the gearspeed the operator wishes to select.

At step 132 the gearshift lever switches are tested to determine if theoperator has moved the gearshift lever to the N position. Assuming hehas not, the test at step 132 proves false and the subsequent test forthe NUP position at step 134 proves true. The program branches back tostep 124 to again test the value in the PSG register and, if it is not18, increment it at step 126 and display the updated value at step 128.

As the displayed value of the PSG register approaches the forward gearwhich the operator wishes to select, he may move the gearshift lever tothe N position in anticipation of stopping the incrementing of the PSGregister when the PSG register is at the desired value. When he doesthis, the program, when it reaches step 132, senses that the gearshiftlever 6 is in the N position and waits.

The program continues to execute step 132 as long as the operator leavesthe gearshift lever in the N position. This enables him to observe thedisplayed preselected gear value and determine if it is higher, lower,or equal to the gear he wishes to select. Assuming first that thedisplayed value is lower than the desired speed, the operator may againmove the gearshift lever to the right to the NUP routine. The programadvances from step 132 through step 134 and back to step 124 again sothat incrementing of the value in the PSG register is resumed.

If the gearshift lever is held too long in the NUP position, the valuein the FG register will reach a count of 18 corresponding to the highestforward gear. When this happens, the test at step 124 proves true andthe program branches directly from step 124 to step 132 so that thesteps 124, 132 and 134 are repeatedly executed as long as the gearshiftlever is held in the NUP position.

If the operator should overshoot the value of the gear he wishes topreselect, he may reduce the value PSG by moving the gearshift lever tothe NDN position. For example, assume that the operator desired topreselect gear 9 but for some reason he holds the gearshift lever in theNUP position too long so that the PSG register is incremented to somevalue greater than 9 before the operator returns the lever to the Nposition. At this point the display 2 is displaying the higher value andthe program is repeatedly executing step 132. When the operator movesthe gearshift lever to the NDN position the program advances to step 134and tests the gearshift switches to see if the gearshift lever is in theNUP position. Since it is not the program advances to step 122' andtests to see if the gearshift lever is in the NDN position. Since it is,the program moves to step 124' where it tests the value in the PSGregister. If the value is not one (representing the lowest forward gear)it is decremented at step 126' and the display is updated at step 128'.

The program then waits at step 130' for a fraction of a second to givethe operator time to move the gearshift lever to the N position if thedisplayed value of PSG is the forward speed which the operator wishes toselect. At step 132' the gearshift switches are tested to see if thegearshift lever is in the N position. If the operator is still holdingthe gearshift lever in the NDN position, the program advances to step134' and loops back to step 124' in preparation for again testing thevalue PSG and decrementing it if it is not one.

If necessary, the operator may again increment the value PSG by movingthe gearshift lever to the N position and then to the NUP position. Theprogram moves from step 132' to step 134' and then through step 122 tostep 124. From this point the incrementing of PSG takes place aspreviously described.

It will be noted that the program steps in right half of FIG. 11 are amirror image of the program steps shown in the left half. The steps inthe left half are executed when the gearshift lever is selectively movedbetween the NUP and N positions to increment the value PSG and the stepsin the right half are executed as the gearshift lever is selectivelymoved between the NDN and N positions to decrement the value PSG. If theoperator has completed his preselection of a gear, he may exit theroutine by moving the gearshift lever to the F or the R position. Whenthe program reaches step 132 and the gearshift lever is in the F or Rposition, the program sequentially executes steps 132, 134 and 122',then exits the routine. On the other hand, if the program reaches step132' and the gearshift lever is in the F or R position, the programsequentially executes steps 132', 134' and 122 before executing step122' and exiting the routine.

The operations described above enable the operator to preselect a singlevalue of PSG. This value determines both the forward gear and thereverse gear which will be selected when the operator moves thegearshift lever from the N position to the F or R position. However, thevalue of PSG may be also used to access a table of reverse gear valuesto obtain a preselected reverse gear. Generally, if PSG is greater thanthe highest reverse gear (12) PSG accesses a location in the table whichstores the value 12, and if PSG is less than the lowest reverse gear (4)PSG accesses a location in the table which stores the value 4. Forvalues between 4 and 12, PSG accesses a table location storing acorresponding value.

Programmable Forward-To-Reverse Speed Selection

Different applications for shuttle shifting have different requirementsfor the forward-to-reverse speed relationship. That is, someapplications may be best performed when the reverse speed is faster thanthe forward speed while others may be best performed when the forwardspeed is faster than the reverse speed, and still other applications arebest performed when the speeds are equal.

In accordance with the principles of the present invention, an operatormay select any one of several modes of operation. That is, he mayprogram microprocessor 1 by operation of the gearshift lever 6 toprovide any one of several reverse gear speeds relative to a forwardgear speed. The relationships are as follows:

R4 (lowest reverse gear) selected regardless of forward gear.

Reverse gear the same speed as forward gear.

Reverse gear 1, 2 or 3 gears faster than forward gear.

Reverse gear 1, 2 or 3 gears slower than forward gear.

FIGS. 12 and 13 illustrate a method whereby, prior to starting theengine, an operator may select a value representing a desired one ofthese forward speed to reverse speed relationships. A ratio value isgenerated and stored and subsequently used by the microprocessor 1 sothat a specific forward to reverse speed relationship is obtained byshuttle shifting between forward and reverse after the engine isstarted. That is, during operation of the vehicle the operator controlsthe selection of forward gear speed while reverse gear speedautomatically is determined by the selected forward gear and the valueRATIO which is preselected prior to starting the engine. The operatorinitiates the forward-to-reverse speed programming mode by holding thegearshift lever in the reverse upshift position (RUP) while turning onthe ignition key. After going through an initialization routine at step110, the microprocessor tests the gearshift switches 4 at step 111 tosee if the gearshift lever is in the RUP position. If it is, the programbranches to step 150 where it gets RATIO and updates the display 2.

RATIO is a value stored in a non-volatile memory location. It representsthe relationship of reverse gear to forward gear.

                  TABLE I                                                         ______________________________________                                        Forward/Reverse Speed Relationships                                           RATIO   -3     -2     -1   0     +1   +2   +3   L                             ______________________________________                                        FG    1     R4     R4   R4   R4    R4   R4   R4   R4                                2     .      .    .    .     .    R4   R5   .                                 3     .      .    .    .     R4   R5   R6   .                                 4     .      .    .    R4    R5   R6   R7   .                                 5     .      .    R4   R5    R6   R7   R8   .                                 6     .      R4   R5   R6    R7   R8   R9   .                                 7     R4     R5   R6   R7    R8   R9    R10 .                                 8     R5     R6   R7   R8    R9    R10  R11 .                                 9     R6     R7   R8   R9     R10  R11  R12 .                                10     R7     R8   R9    R10   R11  R12 .    .                                11     R8     R9    R10  R11   R12 .    .    .                                12     R9      R10  R11  R12  .    .    .    .                                13     .      .    .    .     .    .    .    .                                14     .      .    .    .     .    .    .    .                                15     .      .    .    .     .    .    .    .                                16     .      .    .    .     .    .    .    .                                17     .      .    .    .     .    .    .    .                                18     R9      R10  R11  R12   R12  R12  R12 R4                          ______________________________________                                    

Table I shows the relationship of the reverse gear to a selected forwardgear for each value of RATIO. As shown in Table I, RATIO has one of thevalues -3, -2, -1, 0, +1, +2, +3 or L. If RATIO has the value L, thelowest reverse gear will be selected regardless of the forward gearvalue. If RATIO has the value between -3 and +3, then RATIO is added tothe selected forward gear to determine which reverse gear will beselected. However, if the sum of the forward gear value and RATIO isless than 4, then the lowest reverse gear R4 is selected, and if the sumis greater than 12 then the reverse gear is selected as shown in TableI.

Returning to FIG. 12, after the display is updated at step 150 theprogram moves to step 152 where it waits since the operator is holdingthe gearshift lever in the RUP position. This gives the operator anopportunity to observe the displayed value of ratio and determine if itneeds modification. The operator moves the gearshift lever to the Rposition and the program advances to step 154 where it again waits formovement of the gearshift lever. When the operator moves the gearshiftlever out of the R position, the program advances to an Adjust Ratioroutine 156 illustrated in FIG. 13.

Assume first that the operator, at step 154 moves the gearshift lever tosome position other than an UP or DN position. When the program entersthe Adjust Ratio routine, the tests of the gearshift switches at steps160 and 160' prove false and the program moves back to step 160. Steps160 and 160' are repeatedly executed until the ignition switch is turnedoff or the gearshift lever is moved to an UP or DN position. It shouldbe noted that the selection of a ratio value may be accomplished usingany UP and DN gearshift lever positions. For the sake of simplicity, theflow diagram of FIG. 13 is drawn for the case where the RUP and RDNpositions are used.

Assume now that the value of RATIO displayed at step 150 is lower thanthe value the operator wishes to select so that he moves the gearshiftlever to the RUP position to exit from step 156. In FIG. 13, the RUPtest at step 160 proves true and the program moves to step 162 where ittests the value of RATIO. If ratio is not at its maximum value, it isincremented and saved in a non-volatile memory location at step 164 andthe display updated at 166 before the program moves to step 168.

The routine waits at step 168 for a fraction of a second long enough forthe operator to observe the displayed value of RATIO and move thegearshift lever if he desires to do so. It then advances to step 170 totest the gearshift switches to see if the gearshift lever is in the Rposition. If the operator is still holding the gearshift lever in theRUP position the routine advances to step 172 where the test for the RUPposition proves true. The program loops back to step 162 to test RATIO,increment and save it if it is not at its maximum value, and display theincremented value. This continues until the operator moves the gearshiftlever to the R position. At step 170 the program continuously tests tosee if the gearshift lever is in the R position, and remains at step 170as long as the test proves true. If the operator moves the gearshiftlever from the R position to the RDN position, the program moves fromstep 170; to step 172 where the test for RUP proves false. The programadvances to step 160' and since the gearshift lever is in the RDNposition step 162' is executed where the value of RATIO is tested to seeif it is at its lowest value Assuming it is not, RATIO is decrementedand saved at step 164' and the display updated at step 166'. The programwaits for a fraction of a second at step 168' to permit the operator toobserve the display, and then proceeds to step 170' where the gearshiftswitches are tested to see if the gearshift lever is in the R position.

If the operator has moved the gearshift lever to the R position, theprogram waits at step 170' until he moves the gearshift lever to anotherposition. If he moves the gearshift lever to the RDN position, theprogram advances to step 172', where the RDN test proves true, and loopsback to step 162' to again update the display. On the other hand, if theoperator moves the gearshift lever from the R position to the RUPposition the program moves from step 170' to step 172' and step 160.From step 160 the program tests RATIO and possibly updates it aspreviously described.

Thus, the operator may selectively move the gearshift lever between theR, RDN and RUP positions, the value of RATIO being decremented while thegearshift lever is in the RDN position and incremented when thegearshift lever is in the RUP position. However, as explained above, theFDN, FUP, NUP and NDN positions may also be used forincrementing/decrementing ratio. The flow diagram of FIG. 13 may thus begeneralized by providing UP tests at steps 160 and 172, DN tests atsteps 160' and 172', and N, F or R tests at steps 170 and 170'.

If, during incrementing of RATIO it reaches its maximum value (+3) thetest at step 162 proves true and the program jumps from step 162 to step170, thereby bypassing the incrementing step. In like manner, if RATIOreaches its minimum value (L=4) during decrementing the program jumpsfrom step 162' to step 170' thereby bypassing the decrementing step.

After the operator has adjusted the value of RATIO to the desired value,he may terminate the adjustment by turning the ignition switch off. Theoperator must turn the ignition switch off and then on again, this timenot holding the gearshift lever in the RUP position, in order to use thevalue of RATIO which he has programmed into the system.

After the ignition switch is turned off and then on again to the startposition to start engine 7, the microprocessor begins executing aprogram wherein it samples the gearshift switches and energizes theclutches in transmission 10 as the operator moves the gearshift lever toactuate the switches. Each time the gearshift lever is moved to the Rposition, the microprocessor executes the subroutine shown in FIG. 14a.At step 180 the microprocessor detects from the gearshift switches thatthe gearshift lever has been moved to the R position. At step 182 acurrent gear register CG is tested to see if it contains a value greaterthan 12. The CG register stores the value of the gear (forward) fromwhich the transmission is being shifted. If CG is equal to or greaterthan 12, a previous gear register PG is set to the value 12 at step 184.If CG has a value less than 12 then at step 186 the PG register is setequal to CG. At step 190, PG and RATIO are used to address a tablelocation in memory and read the reverse gear value RG from memory. Thevalue stored in the memory table correspond to the values in Table I,above, for the values of forward gear between 1 and 12. The value of RGis then used by the microprocessor 1 at step 192 to energize theclutches in transmission 10.

Although not part of the illustrated routine of FIG. 14a, it should benoted that upon upshifting or downshifting in reverse, or if speedmatching occurs as subsequently described, the previous gear register PGis cleared.

When the gearshift lever is shifted from reverse to forward, themicroprocessor detects, at step 194 (FIG. 14b), that the lever is in theF position. At step 195, PG is tested to see if it has been cleared. Ifit has, a table is addressed at step 198 to read out the forward gearvalue FG and at step 199 the microprocessor uses this value of FG toenergize the transmission clutches.

On the other hand, if the test at step 195 shows that the PG registerhas not been cleared, then FG is set equal to PG.

From the foregoing description it is seen that the routine illustratedin FIGS. 12 and 13 enables the operator to preselect aforward-to-reverse gear relationship value if he holds the gearshiftlever in the RUP position as he turns the ignition on. FIGS. 14a and 14billustrate how this value is used to modify whatever forward gear valuethe operator happens to select to thereby obtain a reverse gear valuefor controlling transmission 10. The selection of reverse gear is madeaccording to Table I.

Controlled Vehicle Deceleration During Shuttle Shifting

Shuttle shifting of the transmission 10 from forward to reverse gear, orfrom reverse to forward gear results in an energy load on thetransmission oil, and loading of the vehicle engine with a consequentincrease in fuel consumption. The energy load placed on the clutchesincreases at a rate proportional to the square of the vehicle speed sothat when the vehicle speed reaches about 4 MPH the clutches in thetransmission are overloaded by shuttle shifting. Thus, larger and moreexpensive clutches become necessary for shuttle shifting even atmoderate vehicle speeds. However, several methods have been developedfor controlling transmission 10 to prevent clutch overloading and, for agiven clutch sizing, permit shuttle shifting at moderate or high vehiclespeeds without overloading the clutches.

FIG. 15 illustrates a first method which may be used at low and moderatevehicle speeds up to about 7 or 8 miles per hour. Assume that thevehicle has been in some forward gear and the operator moves thegearshift lever 6 (FIG. 10) from the F to the R position. At step 200,the microprocessor senses that the gearshift lever is in the R positionthe program proceeds to step 204 where the microprocessor appliessignals to the clutches in the initial and intermediate clutch sets 70and 75 (FIG. 3) to select the lowest gear speed. At step 206 amodulating signal is applied to the low speed clutch 82 or the reverseclutch 83 in the final clutch set 80. The output shaft 20 is rotating,being driven at this time because of forward vehicle movement.Application of the modulating signal to the clutch in the final clutchset causes the output shaft 20 to begin driving the transmission andthis load begins slowing the output shaft 20. The modulating signal is apulse width modulated current signal that is applied to the solenoidwhich controls the valve that in turn controls the pressure applied tothe torque transmitting element of the clutch.

At step 208, the speed of the output shaft 20 is sensed by sensor 5(FIG. 1) and the microprocessor 1 compares this speed with somethreshold value near zero. If the speed is greater than the thresholdvalue, the microprocessor decreases the modulating signal at step 210and waits for a short interval of time at step 212 before looping backto again execute steps 206 and 208. The decreased modulating signalcauses a higher hydraulic pressure to be applied to the torquetransmitting element of clutch 82.

When the speed of shaft 20 has been reduced so that the sensed speed isless than the threshold value, this condition is detected at step 208and the program moves to step 214 where the microprocessor 1 appliessignals to the clutch sets 70, 75,and 80 to select the desired reversegear speed.

When shifting takes place from reverse to forward gear, themicroprocessor 1 executes a sequence of steps like steps 204-214 withthe exception that the forward gear clutches are set to select thedesired forward gear at step 214.

The method just described permits shuttle shifting of transmissions atlow and moderate speeds even without torque converters. However, thismethod is not satisfactory for use when shuttle shifting at higherspeeds. An incremental increase in efficiency in such operation can begained in the following manner. It has been found that, with properclutch control, clutch energy loads can be reduced thus allowing shuttleshifting to take place at higher speeds while resulting in lower oiltemperatures and lower clutch energy loads. Furthermore, by sharing theenergy load between two or more clutches, shifting may be accomplishedat even higher speeds. Also, there is a reduced engine load and agreater economy of fuel use. To gain all of these advantages, thetransmission 10 illustrated in FIG. 3 may be controlled as illustratedin the flow diagram of FIG. 16 when the gearshift lever 6 (FIG. 1) ismoved into either the reverse position R or the forward position F toselect a new desired gear speed.

At step 220, all of the clutches 71, 72 and 73 in the initial clutch set70 are released thereby disconnecting the engine 7 from thetransmission. Gearing within the transmission continues to rotate. Next,two or more of the clutches 76, 77 and 78 in the intermediate clutch set75 are energized at step 222 thereby locking up the transmission andstopping rotation of the internal transmission parts. After thetransmission has been locked up, one of the clutches 81, 82 and 83 inthe final clutch set is modulated at step 224 to connect thetransmission gearing to the output shaft 20 thereby decelerating thevehicle. The output speed is monitored by the output shaft speed sensor5 (FIG. 1). When the vehicle is nearly stopped, the microprocessoroutputs signals to the clutches in the transmission 10 to actuate theappropriate clutches to select a desired new gear speed. At step 226 themicroprocessor senses the speed and if the speed exceeds a thresholdvalue the microprocessor computes a new modulating signal value at step228 and waits a short interval at step 230. The new modulating signal isthen applied to the solenoid of the clutch in set 80 when the programloops back to step 224. As described above with respect to step 208, thetransmission may then shift to the selected gear.

FIG. 17 illustrates a further method for controlling vehicledeceleration when shuttle shifting. The method illustrated in FIG. 17 isparticularly suited for shuttle shifting at high vehicle speeds. Itallows shuttle shifting at maximum vehicle speed without free wheelingand without excessive clutch loads. The initiation of shifts is based onvehicle speed hence the method automatically adapts to variations invehicle deceleration due to surface conditions, grades, drawbar loadsand operator use of service brakes.

The microprocessor 1 enters the routine of FIG. 17 when the gearshiftlever 6 is in the forward gear position F and the forward speed of thevehicle is above about 7.5 MPH. Actually, the forward speed of thevehicle is determined by the speed sensor 5 which senses the rate ofrotation of the transmission output shaft 20. The shaft carries a72-tooth gear whose rotation is magnetically sensed by the sensor 5which produces one output pulse for each tooth sensed on the rotatinggear. Table II shows, for an exemplary embodiment, the correlationbetween each forward gear and the frequency of the output signal fromthe speed sensor 5.

                  TABLE II                                                        ______________________________________                                        DO NOT        IF FREQUENCY OF                                                 DOWNSHIFT     OUTPUT FROM                                                     FROM          SENSOR EXCEEDS                                                  ______________________________________                                        FG =      18      2802                                                                  17      2392                                                                  16      2043                                                                  15      1724                                                                  14      1472                                                                  13      1257                                                                  12      1067                                                                  11      911                                                                   10      778                                                                    9      662                                                                    8      565                                                                    7      483                                                                    6      408                                                                    5      408                                                                    4      408                                                                    3      408                                                                    2      408                                                         ______________________________________                                    

The routine of FIG. 17 starts at step 250 where the vehicle speed, ormore particularly the output frequency of the sensor 5 is compared witha threshold frequency value. If the sensor output frequency is lowerthan the threshold value it means that another deceleration strategyshould be used. Thus, from step 250 an exit is made from the routine toone of the routines described above for controlling vehicledeceleration.

If the test at step 250 shows that the vehicle speed is high enough toinvoke the high speed deceleration routine, the program moves to step252. At this step, the microprocessor successively accesses its memorywhich stores the values shown in column 2 of Table II, and compares eachaccessed value with the frequency of the output signal from sensor 5until it finds the lowest gear that will not overspeed the engine. Thatis, it finds the highest frequency value in the table which is stillless than the frequency of the output signal from the sensor 5. Forexample, if the output from sensor 5 is a 1400 HZ signal, the value 1257is the highest frequency in the table which is still less than 1400.This corresponds to gear 13. The microprocessor reads this value fromthe table and sends it to the display at step 254. At step 256 the value13 isused to energize the clutches in transmission 10 to select forwardgear 13. Since forward gear 13 would normally drive the shaft 20 at only1257 HZ or 1257×60/72 RPM but the actual rotation of the shaft isgreater, the engine becomes a load which slows down the vehicle.

After the transmission is shifted into gear 13 at step 256, the programenters a loop comprising steps 258 and 260. At step 258 the frequency ofthe output signal from sensor 5 is compared with the threshold frequencyto see if the speed is such that the downshift strategy is stillrequired. If it is not, the routine exits to another decelerationroutine as described above that is suitable for use at lower speeds.

If the test at step 258 shows that the speed is still greater than thethreshold value the program executes step 260. At this step themicroprocessor tests the vehicle speed as measured by the output fromsensor 5 and determines if the transmission can be downshifted one gear.This is done by accessing the table for gear 13 to read out frequencyvalue 1257, and then comparing 1257 with the output frequency asmeasured by sensor 5. If sensor 5 is still producing an output signalgreater than 1257 HZ, the program loops back to again execute steps 258and 260. At some point the vehicle will be decelerated so that theoutput signal from sensor 5 is less than 1257 HZ. When this isdetermined at an execution of step 260, the display is updated at step262 to display gear 12 and at step 264 clutches are energized to selectgear 12 so that the engine 7 again becomes a load on the output shaft20.

Steps 258 and 260 are again repeatedly executed and, if the test at step260 shows the speed as measured by sensor 5 to be less than the valueaccessed from the table, steps 262 and 264 are executed to update thedisplay and downshift the transmission one gear. This continues until atest at step 258 shows that the speed of the vehicle is low enough toemploy a low or medium speed deceleration routine as described above. Atthis point an exit is made from the routine of FIG. 17 to the newdeceleration routine.

Clutch Calibration

As explained above, solenoid operated valves control the hydraulicpressure applied to the clutches and thus the torque transferred by theclutches to move the vehicle. Variations in the current applied to thesolenoids, the valve adjustments, and the pressure required to begin totransfer torque all result in inconsistent operation from one tractor tothe next, and variations in the operation of a given tractor over aperiod of time.

According to one aspect of the present invention, a calibration programis stored in microprocessor 1 for calibrating the clutches in the finalclutch set 80 of transmission 10. This program may be used on each newtractor after assembly, or as required by service or clutch wear, todetermine the magnitude of a current which must be applied to a solenoidso that the clutch controlled by the solenoid produces a torque justsufficient to reduce engine speed. A value representing this magnitudeof current is stored in the microprocessor or memory during thecalibration program. Subsequently, when the solenoid is to be energizedthe value is read from the memory to control the magnitude of thecurrent applied to the solenoid.

FIG. 18 is a flow diagram illustrating one method of clutch calibration.During this method of calibration, the vehicle brakes should be appliedso that the output shaft 20 (FIG. 3) of the transmission does notrotate. This assures uniform loading conditions during the calibrationprocedure. The microprocessor 1 starts the routine at step 300 bysetting I_(S) =I_(M) AX, where I_(M) AX is the maximum current which maybe applied to the solenoid of the clutch being calibrated. At step 301,a current corresponding the value of I_(S) is applied to the solenoid ofthe clutch being calibrated. It should be remembered that the hydraulicpressure applied to one of the clutches in transmission 10 variesinversely with respect to the current I_(S) applied to the clutchsolenoid. Therefor, when I_(S) =I_(M) AX is applied to the clutch atstep 301, the lowest hydraulic pressure is applied to the clutch. Thispressure should be low enough such that the clutch is not applied

At step 302 the routine waits for an interval of time sufficient for theengine speed to stabilize after any loading caused by energization ofthe clutches. After this interval of time has elapsed, the calibrationroutine advances to step 303 where the microprocessor 1 determines theengine speed RPM as sensed by the sensor 9 (FIG. 1). This referencevalue of engine speed is saved and the program advances to step 304where I_(S) is decremented and applied to the clutch being calibrated tothereby increase the pressure to the clutch

At step 305, the program again waits for a sufficient interval of timefor the engine speed to stabilize after any loading caused byapplication of the decremented value of I_(S) to the clutch solenoid atstep 304. At step 306 the engine speed is again sensed and at step 307the new engine speed RPM1 is compared with the reference engine speedRPM. If RPM1 is less than RPM, it means that a reliable calibration ofthe clutch cannot be obtained and servicing of the clutch and/or itscontrols is required The program branches to step 308 where themicroprocessor 1 sends signals to the display 2 to display an error codeindicating a high I_(S) error. After the display is energized thecalibration routine ends.

If the comparison at step 307 shows that RPM1 is not less than RPM thenat step 309 I_(S) is again decremented and applied to the solenoid ofthe clutch being calibrated. The program waits at step 310 for theengine speed to stabilize in case the new value of I_(S) applied to thesolenoid resulted in a loading of the engine as a result of torque beingtransmitted by the clutch. The engine speed is again sensed at step 311and compared at step 312 with the value RPM saved at step 303.

If the comparison at step 312 shows that RPM1 is less than RPM, theprogram moves to step 313 where the value of I_(S) generated at step 309is compared with a minimum permissible value I_(M) IN. If I_(S) is notless than I_(M) IN the program loops back to step 309.

The loop comprising steps 309-313 is repeatedly executed until thecomparison at step 312 shows RPM to be greater than RPM1, or the test atstep 313 shows that I_(S) is less than I_(M) IN. If RPM is greater thanRPM1, it means that the engine has slowed as a result of being loaded,and this in turn indicates that the clutch being calibrated hastransmitted torque in response to the signal I_(S) generated the lasttime step 309 was executed. This value of I_(S) is saved at step 315.Subsequently, each time the clutch is to be energized the microprocessor1 subtracts the saved value of I_(S) from a fixed current value and thedifference current is applied to the clutch as a modulating signal.

If, during execution of the loop comprising steps 309-313, the test atstep 313 proves true, it means that the clutch cannot be calibratedwithout servicing. The microprocessor 1 sends signals to display 2 todisplay a low current error message on the display at step 314.

It will be understood that FIG. 18 illustrates the routine forcalibrating a single one of the clutches 81, 82 or 83. The routine mustbe executed for each clutch to be calibrated so that a calibration valueof I_(S) is saved for each clutch.

For ease of description, steps 307 and 312 show a comparison of RPM andRPM1. However, as is conventional in measurement systems, a small offsetvalue may be added to RPM before it is compared with RPM1. Also, steps304 and 309 show I_(S) being decremented by 1. It should be understoodthat "1" represents an increment of current necessary to change thepressure applied by the clutch torque transmitting element some fixedincrement such as 10psi.

In the calibration method illustrated in FIG. 18, the vehicle brakes areapplied during the calibration procedure to prevent vehicle movement,and the engine speed is sensed to determine when a load is placed on theengine as a result of the clutch transmitting a torque. However, it ispossible to calibrate the clutches by not applying the vehicle brakesduring the calibration procedure, and sensing when the vehicle begins tomove. Vehicle movement may be sensed by sensor 5 (FIG. 1) which sensesrotation of the transmission output shaft 20.

FIG. 19 illustrates the method of calibrating a clutch by sensing whenthe clutch transmits sufficient torque to move the vehicle. At step 320I_(S) is set equal to I_(M) AX so that maximum current is applied to thesolenoid of the clutch being calibrated resulting in minimum hydraulicpressure being applied to the torque transmitting element of the clutch.Clutch solenoids are then energized at step 321 so that drive power fromthe engine may be transmitted to the transmission output shaft 20. Thismay be any combination of clutch solenoids necessary to select aparticular gear, so long as the combination includes the solenoid of theclutch being calibrated. At step 322 the program waits for any torquetransmitted by the clutches to be manifested by movement of the vehicle,or more specifically, rotation of the transmission output shaft 20. Atstep 323 the microprocessor 1 acts with sensor 5 to sense rotation ofthe shaft 20. If it is rotating at this time it means that it isimpossible to calibrate the clutch so the program branches to step 329where the microprocessor sends signals to the display 2 to cause it todisplay an out of range error code.

If the test at step 323 shows that output shaft 20 is not rotating, theprogram decrements I_(S) at step 324 and applies this decremented valueof I_(S) to the solenoid of the clutch being calibrated. This causes anincrease in the hydraulic pressure applied to the torque transmittingelement of the clutch. At step 325 the program waits for this increasedpressure to take effect and at step 326 the output shaft rotation isagain sensed.

Assuming that shaft 20 is still not rotating, the program advances tostep 327 to compare the value of I_(S) produced at step 324 with aminimum permissible solenoid current I_(M) IN. If I_(S) is not less thanI_(M) IN the program loops back to step 324. The loop comprising steps324-327 is repeatedly executed and I_(S) is decremented on eachexecution until one of the tests at step 326 or 327 proves true.

When the test at step 326 indicates that shaft 20 is rotating, the lastvalue of I_(S) produced at step 324 is saved in memory at step 328 andthe program ends. This value of IS may subsequently be used to controlthe magnitude of the current applied to the clutch.

If the program should execute the loop comprising steps 324-327 so manytimes that I_(S) is decremented to a value less than I_(M) IN the clutchcannot be calibrated. Step 327 detects that I_(S) is less than I_(M) INand the program moves to step 329 where an out of range error code issent to display 2 before the program ends.

Manual Override of Automatic Ratio Matching

The prior art transmission control system shown in FIG. 1 employs anautomatic ratio matching feature to reduce clutch slippage when shiftinggears, or to prevent start-up in a high gear which could overload theclutches. In addition, the automatic ratio matching feature permitsdirect shifting from one gear to another without shifting through all ofthe intermediate gears.

In FIG. 1 the microprocessor 1 invokes a ratio matching routine when thegearshift lever 6 is moved to the neutral position or when the clutchpedal 3 is depressed. The microprocessor 1 computes a speed ratio basedon the rates of rotation of input shaft 15 and output shaft 20 as sensedby the sensors 9 and 5, respectively, and energizes the display 2 toindicate the optimum gear for the computed ratio. The computation isrepeated and the display updated as long as pedal 3 is depressed or thegearshift lever 6 is in the neutral position. When the pedal 3 isreleased and the gearshift lever 6 is moved to the forward or thereverse position, the microprocessor 1 sends signals to the clutches 8to select the gear corresponding to the gear displayed on the display 2.

While the automatic ratio matching feature is admirably suited for itsintended purpose, it does remove some control of the transmission 10from the operator. FIG. 20a is a flow diagram illustrating a method formanually overriding the automatic ratio matching feature of the systemof FIG. 1. The microprocessor 1 invokes the routine of FIG. 20a when itsenses, at step 400, that the clutch pedal 3 has been depressed toactuate the clutch pedal switch CPSW, or the gearshift lever is in theneutral position N. At step 401, the microprocessor updates the display2 and sets a timer. At steps 402 and 404, the microprocessor determinesfrom the gearshift switches 4 whether the gearshift lever 6 is in one ofthe upshift or downshift positions Assume for the moment that it is not.The program checks the timer at step 406 to see if 0.1 second haselapsed since the timer was set at step 401. The program loops 10 backand repeats steps 402, 404 and 406 until the 0.1 second intervalexpires. This gives the operator time to operate the gearshift lever ifhe wishes.

When the 0.1 second interval expires, the program advances to step 408to calculate the ratio between the rate of rotation of output shaft 20and input shaft 15. This ratio defines the gear which will be selectedwhen the gearshift lever 6 is moved out of the neutral position or theclutch pedal 3 is released At step 410 the display 2 is updated todisplay the gear value.

At step 412, the microprocessor tests the gearshift switches 4 and theclutch pedal switch CPSW. If the clutch pedal is still depressed and thegearshift lever is still in the neutral position, the program loops backto step 402 to repeat the operations just described.

Should the operator release the clutch pedal and shift the gearshiftlever out of neutral, automatic ratio matching is effective. At step 412an exit is made from the routine to set the clutches to the gearcorresponding to the gear last displayed at step 410.

In accordance with the invention, the steps 402 and 404 are provided topermit the operator to override the automatic ratio matching operation.The override may take place any time after the routine is entered butbefore the clutch pedal is released and the gearshift lever is moved outof neutral. The override is effected when the operator moves thegearshift lever to an upshift or a downshift position. If the gearshiftlever is moved to an upshift position an exit is made from the routineat step 402 to an upshift routine and if it is moved to a downshiftposition an exit is made from the routine at step 404 to a downshiftroutine.

The manual override method illustrated in FIG. 20a is permanent in thatautomatic ratio matching will not occur again until the next time thegearshift lever 6 is shifted to the neutral position or the clutch pedal3 is depressed. FIG. 20b illustrates a manual override method which istemporary in that the automatic ratio matching starts again if thegearshift lever remains in neutral or the clutch pedal remains depressedfor a specific interval of time.

The routine of FIG. 20b is entered at step 420 when the microprocessorsenses that the operator has depressed the clutch pedal or shifted thegearshift lever into neutral. At step 422 the display is updated and a0.1 second timer is reset. Tests are then made at steps 424 and 426 tosee if the gearshift lever has been shifted to an upshift or a downshiftposition. Assuming for a moment that the gearshift lever has not beenmoved to an upshift or a downshift position, the program advances tostep 428 and tests the 0.1 second timer to see if it has timed out. Ifit has not, the program branches back to step 424 to repeat the loopcomprising steps 424, 426 and 428 until the 0.1 second interval haselapsed.

At the end of the 0.1 second interval the microprocessor tests a 1second timer at step 430 to see if it is running. This timer is set assubsequently explained and for the moment assume that it is not running.The program proceeds to step 432 to calculate a ratio as explainedpreviously with respect to step 408 of FIG. 20a. At step 434 thecalculated ratio value is used to update the display, thereby indicatingto the operator the gear which will be selected when he moves thegearshift lever out of neutral or releases the clutch pedal.

At step 436 the clutch pedal switch and gearshift lever switches aretested and, if the operator has not released the clutch pedal or has notshifted out of neutral, the program branches back to step 422 to repeatthe sequence of operations just described. If the operator should movethe gearshift lever out of neutral, or release the clutch pedal, theprogram exits the routine at step 436 and proceeds to complete theautomatic ratio matching by setting the clutches in the transmission toselect the gear corresponding to the gear value last displayed at step434.

Assume now that while the microprocessor is still executing the loopextending from step 424 to step 436, the operator moves the gearshiftlever to the upshift or downshift position. If he moves it to theupshift position the program branches to step 440 to increment the gearselection value being displayed on the display 2, and if he moves it tothe downshift position the program branches to step 442 to decrement thedisplayed gear selection value. After step 440 or 442 is executed, themicroprocessor updates the display at step 444 and sets a timer at step446.

The timer set at step 446 is the timer which is tested at step 430. Whenthe timer is set, it runs for one second. During this one secondinterval the test at step 430 will prove true and the microprocessorwill skip steps 432 and 434 thus bypassing the calculation and displayof the automatic ratio matching gear.

After step 446 is executed, the program proceeds to step 436 to see ifthe clutch pedal is released and the gearshift lever has been shiftedout of neutral. If it has, then the program exits the routine at step436 and proceeds to select the gear corresponding to the gear valuedisplayed at step 444.

To summarize the operations in FIG. 20b, if the routine is entered and,during execution of the routine, the gearshift lever is not shifted toone of the upshift or downshift positions, normal automatic ratiomatching occurs when the test at step 436 shows that the gearshift leveris not in neutral and the clutch pedal is released.

On the other hand, if the operator moves the gearshift lever to adownshift or upshift position he may increment or decrement thedisplayed gear value. He may increment or decrement by more than one byholding the gearshift lever in the upshift or downshift position. He mayeven increment or decrement the displayed gear value, shift thegearshift lever to neutral, and then shift it back to one of the upshiftor downshift positions so long as he does not leave the gearshift leverin neutral long enough for the one-second timer to time out. If heshould permit the timer to time out, steps 432 and 434 would no longerbe bypassed and the automatic ratio matching would again be in effect.Even at this point he may again override the automatic ratio matchingfeature by again moving the gearshift lever to the upshift or downshiftposition. When step 436 detects that the gearshift lever is not inneutral and the clutch pedal is not depressed, the transmission isshifted into the gear whose value was last displayed at step 434 or 444.the value displayed at step 434 is used if the gearshift lever has notbeen moved to the upshift or downshift position while the routine wasbeing executed, or if more than one second has elapsed since thegearshift lever was last in the upshift or downshift position. The valuedisplayed at step 444 is used only if the clutch pedal is released andthe gearshift lever is shifted out of neutral within one second of thetime the value is first displayed.

It will be understood that changes in the details, materials, steps, andarrangements of parts which have been described and illustrated toexplain the nature of the invention will occur to and may be made bythose skilled in the art upon a reading of this disclosure within theprinciples and scope of the invention. The foregoing descriptionillustrates the preferred embodiment of the invention; however,concepts, as based upon the description may be employed in otherembodiments without departing from the scope of the invention.Accordingly, the following claims are intended to protect the inventionbroadly as well as in the specific form shown.

Having thus described the invention, what is claimed is:
 1. A method ofcalibrating clutches in a transmission operably connected to an engineand having said clutches for selectively interconnecting an input driveshaft, an output drive shaft, and a plurality of gears rotatably housedin said transmission in driving relationship with said input and outputdrive shafts such that a selective engagement of said clutches willeffect a varying of the speed of operation of said output shaft for agiven speed of operation of said input shaft, said transmission furtherhaving an electrical control system including a microprocessorresponsive to switches actuated by manual movement of a gearshift leverbetween a plurality of positions for controlling said clutches in thetransmission, said clutches being operably connected to a hydraulicsystem for effecting the actuation of each respective said clutch by anincrease in hydraulic pressure for each said clutch as controlledthrough operation of said microprocessor, the methodcomprising:restraining said output shaft from rotation; determining areference engine speed; applying an increment of hydraulic pressure to aselected one of said clutches; after said applying step, sensing thecurrent speed of operation of said engine; after said sensing step,comparing said current engine speed to said reference engine speed;repeating said applying, sensing, and comparing steps until said currentengine speed is less than said reference engine speed, therebyindicating that said engine is being loaded; and storing in saidmicroprocessor a value corresponding to the hydraulic pressure requiredto start loading of said engine.
 2. The method of claim 1 furthercomprising the step of:waiting for an interval of time after saidapplying step to permit the speed of operation of said engine tostabilize before effecting said sensing step.
 3. The method of claim 2wherein the hydraulic pressure to each said clutch is controlled by anelectrically actuated solenoid valve operably connected to saidelectrical control system such that the value of the hydraulic pressureapplied to each respective clutch is proportionate to the electricalcurrent applied to the corresponding solenoid valve from said electricalcontrol system, said applying step including the step of:changing theamount of electrical current to the corresponding solenoid valve by apreselected increment.
 4. The method of claim 3 wherein the value of thehydraulic pressure applied to each respective clutch is indirectlyproportional to the amount of electrical current applied to thecorresponding solenoid valve, said changing step including the stepof:decrementing the amount of current applied to the corresponding saidsolenoid valve by a preselected increment.
 5. The method of claim 4wherein said determining step is applied with said output shaft beingdisengaged from said input shaft so that said reference engine speed isdetermined without load being applied to said engine.
 6. The method ofclaim 5 wherein the first application of said comparing step includesthe step of:ending the calibration of the selected said clutch if saidcurrent engine speed is less then said reference engine speed.
 7. Amethod of calibrating clutches in a transmission operably connected toan engine and having said clutches for selectively interconnecting aninput drive shaft, an output drive shaft, and a plurality of gearsrotatably housed in said transmission in driving relationship with saidinput and output drive shafts such that a selective engagement of saidclutches will effect a varying of the speed of operation of said outputshaft for a given speed of operation of said input shaft, saidtransmission further having an electrical control system including amicroprocessor responsive to switches actuated by manual movement of agearshift lever between a plurality of positions for controlling saidclutches in the transmission, said clutches being operably connected toa hydraulic system for effecting the actuation of each respective saidclutch by an increase in hydraulic pressure for each said clutch ascontrolled through operation of said microprocessor, the methodcomprising:restraining said output shaft from rotational movement;running said engine in a no-load condition and determining a referenceengine speed corresponding to said no-load condition; incrementallyincreasing the hydraulic pressure for a selected clutch while all otherappropriate clutches are engaged to permit a transfer of rotation powerfrom said engine driven input shaft to said output shaft through saidselected clutch when said selected clutch becomes engaged; and recordinga value corresponding to the hydraulic pressure required to effectengagement of said selected clutch, determined by a loading of saidengine as measured by a decrease of said current engine speed below saidreference engine speed.
 8. The method of claim 7 wherein saidincrementally increasing step includes the steps of:applying hydraulicpressure to the selected said clutch greater than the hydraulic pressurepreviously applied by an incremental amount; after each applying stepproviding an incremental increase in hydraulic pressure to the selectedsaid clutch, sensing the engine speed to define a current engine speed;after each said sensing step, comparing the current engine speed to saidreference engine speed; and repeating said applying, sensing, andcomparing steps until said current engine speed is less than saidreference engine speed, thereby indicating that said engine is beingloaded.
 9. The method of claim 8 wherein the hydraulic pressure to eachsaid clutch is controlled by an electrically actuated solenoid valveoperably connected to said electrical control system such that the valueof the hydraulic pressure applied to each respective clutch isindirectly proportionate to the electrical current applied to thecorresponding solenoid valve from said electrical control system, saidapplying step including the step of:decrementing the amount ofelectrical current applied to the corresponding said solenoid valve by apreselected increment.
 10. The method of claim 9 further comprising thestep of:waiting for an interval of time after each said applying step topermit the speed of operation of said engine to stabilize beforeeffecting said sensing step.